Ignored stream backpressure causes event-loop stalls

Ignoring backpressure in streams builds up buffers and creates bursts of work that block the event loop during flush/drain cycles. Request rate metrics don't show buffer health or saturation.

Instrument writableLength/highWaterMark saturation, stream pipeline duration, time spent in transform functions, and dropped chunks. Use pipeline() with proper error handling to manage backpressure correctly.